Altogether, 660 people including doctors, teachers and former police officers have been arrested in the biggest ever UK crackdown on obscene images of children, the National Crime Agency said.

A Norfolk Constabulary spokesman confirmed that seven men in the county had been arrested.

This includes three from the King’s Lynn area, aged 52, 41 and 51, a 29-year-old from Thetford, and three from the Norwich area, aged 55, 68 and 44. In Suffolk, those arrested included a 45-year-old man from Beccles and an 18-year-old man from Lowestoft.

A spokesman for Norfolk and Suffolk Constabulary said: “In total across Norfolk and Suffolk 347 computers and related equipment such as storage devices were seized along with 36 mobile phones. All suspects have been bailed pending further enquiries.”

The unprecedented six-month operation headed by the NCA saw 660 people held for downloading and sharing the sickening pictures, and has already led to charges for serious sexual assault.

Those arrested included a doctor who had access to more than one million depraved pictures, was found to have met up with boys and kept sex aids and rope in the boot of his car.

Scout leaders and care workers were also among the huge number of people held across England, Wales, Scotland and Northern Ireland, and the vast majority had never before aroused suspicion.

The massive investigation, involving all 45 British police forces, led to 431 children who were in the “care, custody or control” of the suspects being “safeguarded”, including 127 who were identified as being at serious risk of harm. Those arrested had used the internet or the so-called “dark web” - internet content that is not listed for access by normal search engines.

The NCA would not reveal the precise tactics it had used, but in previous child abuse cases officers have gone undercover and posed as potential victims to lull sex offenders into showing their true colours.

Norfolk’s chief constable Simon Bailey, who is the national lead for child abuse investigations, said that police can track paedophiles online, even when using the dark web.

“Law enforcement now has the capability to see what people are doing,” he said. “Six hundred and sixty people have currently been arrested, there will be more arrests. There is a clear message to anybody using the internet to facilitate and to commit this type of crime that you are vulnerable.”

There were only 39 registered sex offenders among those arrested, with the majority able to avoid detection until now. So far officers have searched 833 properties and examined 9,172 computers, phones and hard drives.